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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 397 records · Page 22
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Measuring type Ia supernova angular-diameter distances with intensity interferometry

This paper investigates the potential of intensity interferometry, based on the Hanbury Brown-Twiss effect, for measuring supernova sizes and distances. With optimized telescope positioning, observing strategy, and advancements in single-photon detection technology, this method can provide precise angular size measurements of supernovae with apparent magnitudes as bright as 12 mag. For type Ia supernovae, this limiting brightness corresponds to a local volume extending to redshift z∼0.004 and an anticipated discovery rate of approximately 1 event per year. The combination of angular size data with known physical dimensions enables accurate distance determination. Multiple telescope pairs at different relative positions allow tomographic mapping of the ejecta structure while reducing distance uncertainties. As type Ia supernovae serve as standardizable candles for measuring the Universe’s expansion history, combining intensity interferometry distances with the supernova Hubble diagram facilitates measurements of the Hubble constant H0.

cosmological parameters↗
NASA NTRS1979

Synchronization of clocks by very-long-baseline interferometry

Two hydrogen-maser clocks, one at Haystack Observatory and one at the National Radio Astronomy Observatory, were synchronized by means of observations of several extragalactic radio sources on March 28, and again on September 23, 1977. Observations were made sequentially in eight 360-kHz bands distributed between about 8.4 and 8.5 GHz with spacings designed to enable the group-delay difference between the signals received at the two observatories from a given source to be estimated unambiguously, within an uncertainty of less than 1 ns set by receiver noise. The epoch and the rate differences between the observatories' clocks for each experiment were estimated by analysis of observations that spanned several hours. The application of corrections for the contributions to the delays of the antennas, feeds, receiver systems, and recorders yielded absolute determinations of the clock epoch differences. During each experiment, portable cesium clocks were flown from the U.S. Naval Observatory to the observatories and back. The traveling-clock data, analyzed in each case after the VLBI synchronization had been completed, confirmed the VLBI results to within 18 and 14 ns for the first and second experiments, respectively.

Clark, T. A.↗
NASA NTRS1989

Orbital elements of Charon from speckle interferometry

The semimajor axis and the inclination are the two most important quantities presently determined from 56 well-calibrated speckle-interferometric observations of the position of Charon, which are presented in conjunction with an orbit solution that incorporates them. Both values in the best solution obtained are noted to significantly differ from earlier determinations. The new value for the semimajor axis represents a 2.7 percent increase over the previously accepted value; the mean density of the system, however, remains unaltered.

Beletic, J. W.↗
NASA NTRS1992

The orbit of Alpha Equulei measured with long-baseline optical interferometry - Component masses, spectral types, and evolutionary state

The apparent orbit of the double-lined spectroscopic binary Alpha Equulei was measured using observations, from June 13, 1989 to September 15, 1990, with the Mark III Optical Interferometer. The results, combined with the spectroscopic results of Rosvick and Scarfe (1991), were used to obtain estimates of the masses of the components, their absolute magnitudes, and the distance to the system. In addition, the magnitude differences between the components were determined at four wavelengths; these were combined with the colors reported by Stickland (1976) to derive colors for the two Alpha Equulei components and to estimate their spectral types.

Armstrong, J. T.↗
NASA NTRS2023

Single-Band VLBI Absolute Astrometry

The ionospheric path delay impacts single-band very long baseline interferometry (VLBI) group delays, which limits their applicability for absolute astrometry. I consider two important cases: when observations are made simultaneously in two bands, but delays in only one band are available for a subset of observations and when observations are made at one band design. I developed optimal procedures of data analysis for both cases using Global Navigation Satellite System (GNSS) ionosphere maps, provided a stochastic model that describes ionospheric errors, and evaluated their impact on source position estimates. I demonstrate that the stochastic model is accurate at a level of 15%. I found that using GNSS ionospheric maps as is introduces serious biases in estimates of declination and I developed a procedure that almost eliminates them. I found serendipitously that GNSS ionospheric maps have multiplicative errors and have to be scaled by 0.85 in order to mitigate the declination bias. A similar scale factor was found in comparison of the vertical total electron content from satellite altimetry against GNSS ionospheric maps. I favor interpretation of this scaling factor as a manifestation of the inadequacy of the thin shell model of the ionosphere. I showed that we are able to model the ionospheric path delay to the extent that no noticeable systematic errors emerge and we are able to assess adequately the contribution of the ionosphere-driven random errors on source positions. This makes single-band absolute astrometry a viable option that can be used for source position determination.

Radio astrometry↗
NASA NTRS1994

Morphological changes in the NGC 6251 jet

The giant radio galaxy NGC 6251 is a particularly good object for observational tests of relativistic jet models. Due to its high declination and approximately 0.5 Jy radio nucleus, high-quality Very Long Baseline Interferometry (VLBI) images of the central regions of the source can be made with northern hemisphere arrays. In addition, the large-scale radio morphology strongly suggests that the radio axis lies close to the plane of the sky, so Doppler boosting should be less extreme than in the core-dominated superluminal sources. Earlier 18 cm VLBI observations of NGC 6251 revealed an unexpectedly large jet/counterjet brightness ratio and small transverse motion of a feature in the parsec-scale jet. These early results are difficult to reconcile with the simplest symmetric relativistic jet models. In this paper we present a third-epoch 18 cm VLBI image of the parsec-scale radio jet in NGC 6251, and compare jet morphology over a 5 year time span. The jet shows a minor brightness peak at nearly the same distance from the core as the '25 mas knot' seen in the first- and second-epoch VLBI images. This feature is much less pronounced in the third epoch, and a relatively bright, new knot has appeared approximately 12 mas from the core. If this new component had a constant brightness during the 5 years separating the first and third observing epochs, then it must have moved away from the core with an apparent speed of at least 1.2c (compared with an upper limit of 0.23c for motion of the 25 mas knot). However, we cannot yet rule out a local brightening of the inner jet in favor of a new moving component. We determine a lower limit for the jet/couterjet brightness ratio of 100:1 within 6 mas of the core. We also present a new Very Large Array (VLA) image of the kpc-scale jet with 3 sec resolution, made from data obtained during the VLBI observations. The rate of decrease in jet surface brightness from parsec to kiloparsec scales is similar to jets in known superluminal radio sources.

Jones, Dayton L.↗
NASA NTRS2000

The SRTM sub-arcsecond metrology camera

This paper provides a description of the metrology camera, the process used to prepare it for flight on SRTM, the LED target development effort, test and alignment issues, and the observed in-flight performance.

metrology interferometry SRTM↗
DOE OSTI2021

TIC 168789840: A Sextuply Eclipsing Sextuple Star System

We report the discovery of a sextuply eclipsing sextuple star system from TESS data, TIC 168789840, also known as TYC 7037-89-1, the first known sextuple system consisting of three eclipsing binaries. The target was observed in Sectors 4 and 5 during Cycle 1, with lightcurves extracted from TESS Full Frame Image data. It was also previously observed by the WASP survey and ASAS-SN. The system consists of three gravitationally bound eclipsing binaries in a hierarchical structure of an inner quadruple system with an outer binary subsystem. Follow-up observations from several different observatories were conducted as a means of determining additional parameters. The system was resolved by speckle interferometry with a 0.″42 separation between the inner quadruple and outer binary, inferring an estimated outer period of ∼2 kyr. It was determined that the fainter of the two resolved components is an 8.217 day eclipsing binary, which orbits the inner quadruple that contains two eclipsing binaries with periods of 1.570 days and 1.306 days. Markov Chain Monte Carlo (MCMC) analysis of the stellar parameters has shown that the three binaries of TIC 168789840 are “triplets,” as each binary is quite similar to the others in terms of mass, radius, and T {sub eff}. As a consequence of its rare composition, structure, and orientation, this object can provide important new insight into the formation, dynamics, and evolution of multiple star systems. Future observations could reveal if the intermediate and outer orbital planes are all aligned with the planes of the three inner eclipsing binaries.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2025

Fundamental physics opportunities with future ground-based mm/sub-mm VLBI arrays

The Event Horizon Telescope (EHT) Collaboration recently published the first images of the supermassive black holes in the cores of the Messier 87 and Milky Way galaxies. These observations have provided a new means to study supermassive black holes and probe physical processes occurring in the strong-field regime. We review the prospects of future observations and theoretical studies of supermassive black hole systems. Current ground-based very-long-baseline interferometry (VLBI) arrays like the EHT and proposed future extensions like the next-generation Event Horizon Telescope will greatly enhance the capabilities of black-hole imaging interferometry. These enhancements will open up several previously inaccessible avenues of investigation, thereby providing important new insights into the properties of supermassive black holes and their environments. This review describes the current state of knowledge for five key science cases, summarising the unique challenges and opportunities for fundamental physics investigations that future mm/sub-mm VLBI developments will enable.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
NASA NTRS1996

Detecting Small-Scale topographic Changes and Relict Geomorphic Features on Barrier Islands using SAR

The shapes and elevations of barrier islands may change dramatically over a short period of time such as during a storm. Even between storms, sediment is constantly shifting to and from these islands and between different areas of the islands at varying rates and in varying amounts. Coastal scientists and engineers, however, are currently unable to measure these changes occurring over an entire barrier island at once. This three-year project, which is funded by NASA and jointly conducted by the Bureau of Economic Geology and the Center for Space Research at The University of Texas at Austin, is designed to overcome this problem by developing the use of interferometry from airborne synthetic aperture radar (AIRSAR) to detect changes in coastal topography. Surrogate measures of topography observed in fully polarimetric AIRSAR are also being investigated.

Gibeaut, James C.↗
NASA NTRS2021

TIC 168789840: A Sextuply Eclipsing Sextuple Star System

We report the discovery of a sextuply eclipsing sextuple star system from TESS data, TIC 168789840, also known as TYC 7037-89-1, the first known sextuple system consisting of three eclipsing binaries. The target was observed in Sectors 4 and 5 during Cycle 1, with light curves extracted from TESS Full Frame Image data. It was also previously observed by the WASP survey and ASAS-SN. The system consists of three gravitationally bound eclipsing binaries in a hierarchical structure of an inner quadruple system with an outer binary subsystem. Follow up observations from several different observatories were conducted as a means of determining additional parameters. The system was resolved by speckle interferometry with a 0 42 separation between the inner quadruple and outer binary, inferring an estimated outer period of ∼2 kyr. It was determined that the fainter of the two resolved components is an 8.217 day eclipsing binary, which orbits the inner quadruple that contains two eclipsing binaries with periods of 1.570 days and 1.306 days. Markov Chain Monte Carlo (MCMC) analysis of the stellar parameters has shown that the three binaries of TIC 168789840 are “triplets,” as each binary is quite similar to the others in terms of mass, radius, and Teff. As a consequence of its rare composition, structure, and orientation, this object can provide important new insight into the formation, dynamics, and evolution of multiple star systems. Future observations could reveal if the intermediate and outer orbital planes are all aligned with the planes of the three inner eclipsing binaries.

Brian P. Powell↗
NASA NTRS2018

VLTI-GRAVITY Measurements of Cool Evolved Stars I. Variable Photosphere and Extended Atmosphere of the Mira Star R Peg

Context. Dynamic model atmospheres of Mira stars predict variabilities in the photospheric radius and in atmospheric molecular layers which are not yet strongly constrained by observations. Aim. Here we measure the variability of the oxygen-rich Mira star R Peg in near-continuum and molecular bands. Methods. We used near-infrared K-band spectro-interferometry with a spectral resolution of about 4000 obtained at four epochs between post-maximum and minimum visual phases employing the newly available GRAVITY beam combiner at the Very Large Telescope Interferometer (VLTI). Results. Our observations show a continuum radius that is anti-correlated with the visual lightcurve. Uniform disc (UD) angular diameters at a near-continuum wavelength of 2.24 m are steadily increasing with values of 8.7 0.1 mas, 9.4 0.1 mas, 9.8 0.1 mas, and 9.9 0.1 mas at visual phases of 0.15, 0.36, 0.45, 0.53, respectively. UD diameters at a bandpass around 2.05 m, dominated by water vapour, follow the near-continuum variability at larger UD diameters between 10.7 mas and 11.7 mas. UD diameters at the CO 2-0 bandhead, instead, are correlated with the visual lightcurve and anti-correlated with the near-continuum UD diameters, with values between 12.3 mas and 11.7 mas. Conclusions. The observed anti-correlation between continuum radius and visual lightcurve is consistent with an earlier study of the oxygen-rich Mira S Lac, and with recent 1D CODEX dynamic model atmosphere predictions. The amplitude of the variation is comparable to the earlier observations of S Lac, and smaller than predicted by CODEX models. The wavelength-dependent visibility variations at our epochs can be reproduced by a set of CODEX models at model phases between 0.3 and 0.6. The anti-correlation of water vapour and CO contributions at our epochs suggests that these molecules undergo different processes in the extended atmosphere along the stellar cycle. The newly available GRAVITY instrument is suited to conducting longer time series observations, which are needed to provide strong constraints on the model-predicted intra- and inter-cycle variability.

photospheric radius↗
DOE OSTI2022

Photovoltaic module antireflection coating degradation survey using color microscopy and spectral reflectance

Abstract Commercial antireflective coatings (ARCs) on photovoltaic (PV) module glass can improve module power by 2.5%–3.0%, but their long‐term field performance requires additional study. In this paper, we investigate ARC performance on fielded modules using two nondestructive techniques: reflectance spectroscopy and RGB microscopy, finding a large variation in coating durability and performance. For new coatings, the fleet average nominal power enhancement is 2.8%. This power enhancement is observed to degrade at approximately −0.05%/year absolute over the first 8 years of fielding in arrays that are not regularly cleaned. Interferometry and imaging results imply that coating loss for these modules is due to slow chemical thinning of the initial 125 nm thick coating by 1.4 to 5.0 nm/year. Due to the physics of interference coatings, the performance loss is projected to accelerate as the coating is further thinned, resulting in a coating lifetime (time to 80% of initial performance) of 7.5 to 25 years. At the higher 5.0 nm/year coating loss rates, we estimate that −0.14%/year power degradation of the module can be attributed solely to ARC degradation over the first 20 years. Extreme coating loss is observed on some modules where after 8 years fielding, the coating can be completely removed with a single wet wipe with a lens tissue. A case study is also presented comparing ARC and noncoated modules installed at a single site in 2013. We find that the ARC modules have a 2.6% higher soiling power loss than the noncoated modules; this exceeds the ARC power enhancement of 2.4% and leads to the surprising conclusion that the ARC lowers production for modules in this location due to increased soiling. These results demonstrate that RGB microscopy is a powerful, field‐capable, and quantitative characterization technique for assessing degradation of PV module ARCs.

Karin, Todd↗
NASA NTRS1972

Very long baseline interferometry

Some astronomical results, obtained by very long baseline interferometry, on quasi-stellar sources are reported. Data cover variations in optical luminosity, radio brightness variations, and observations of quasi-stellar nuclei.

Clark, T.↗
NASA NTRS1976

A demonstration of an independent-station radio interferometry system with 4-cm precision on a 16-km base line

Radio interferometry promises eventually to measure directly, with accuracies of a few centimeters, both whole earth motions and relative crustal motions with respect to an 'inertial' reference frame. Interferometry measurements of arbitrarily long base lines require, however, the development of new techniques for independent-station observation. In connection with the development of such techniques, a series of short base line demonstration experiments has been conducted between two antennas. The experiments were related to a program involving the design of independent-station instrumentation capable of making three-dimensional earth-fixed base line measurements with an accuracy of a few centimeters. Attention is given to the instrumentation used in the experiments, aspects of data analysis, and the experimental results.

Thomas, J. B.↗
NASA NTRS1978

Present status and future prospects for NASA's program in geodynamics

An overview of NASA's involvement in developing systems for precise determination of polar motion, earth rotation, and position on the earth's surface is given. The observational methods discussed are laser ranging to the moon and to artificial satellites, and very long baseline microwave interferometry. A plan for a geodynamics program to apply space technology to research in earth dynamics is outlined.

Flinn, E. A.↗
NASA NTRS1986

Precise interferometric tracking of the DSCS II geosynchronous orbiter

A demonstration of the precise tracking of a geosynchronous orbiter by radio metric techniques based on very-long-baseline interferometry (VLBI) has been jointly conducted by the Jet Propulsion Laboratory and Japan's Radio Research Laboratory. Simultaneous observations of a U.S. Air Force communications satellite from tracking stations in California, Australia, and Japan have determined the satellite's position with an accuracy of a few meters. Accuracy claims are based on formal statistics, which include the effects of errors in non-estimated parameters and which are supported by a chi-squared of less than one, and on the consistency of orbit solutions from disjoint data sets. A study made to assess the impact of shorter baselines and reduced data noise concludes that with a properly designed system, similar accuracy could be obtained for either a satellite viewed from stations located within the continental U.S. or for a satellite viewed from stations within Japanese territory.

Border, J. S.↗